The quantity of phosphorus in effluent water from residences is often the factor which limits the concentration of residences that can be accommodated around the banks of a lake. Too much phosphorus in the lake water leads to a nutrient imbalance, a depletion of the oxygen content of the water, a damaging effect on the fish population, and other effects.
In order to permit more residences around the lake, or to enable the water of the lake to be kept clean, a system for removing the phosphorus from the effluent water is desirable. The invention is aimed at providing a more practical and cost-effective system for removing phosphorus from effluent water than has been available hitherto.